During drilling operations for the production of hydrocarbons, different earthen formations may be encountered along the wellbore. Certain formations may have a high amount of structural integrity, such that the wellbore through those formations has a diameter approximately equal to the full gage diameter of the drill bit used to drill the wellbore. However, other formations may have a lower amount of structural integrity due to being composed of softer materials (e.g., carbonates, clay). These softer formations are susceptible to breaking up or crumbling during drilling operations, creating a larger-diameter portion of the wellbore. Thus, the wellbore may take on an irregular, corrugated profile (a “rugose” bore) as a result of certain areas having a diameter approximately equal to the full gauge diameter of the drill bit and other areas having a larger diameter due to crumbling of the formation material.
In some situations, a logging toolstring may be conveyed into the wellbore (e.g., on the end of a wireline, coiled tubing, or drill pipe) to gather data, which may include common measurements such as pressure or temperature, or more advanced measurements such as rock properties, fracture analysis, fluid properties in the wellbore, or formation properties extending into the rock formation. However, the logging tool may not pass through rugose sections of the wellbore. If the logging tool becomes stuck, the tool may have to be retrieved and returned. The logging tool may be returned, for example, by using a tractor to push the tool downhole or by placing the logging tool at the end of a pipe string (e.g., drill string), both of which are time-consuming and costly. Alternately, the wellbore may be “cleaned” by circulating mud and a wiper tip through the wellbore, which is also time-consuming and introduces a further cost.
Accordingly, there remains a need in the art for devices and methods for guiding and navigating tools through rugose boreholes. Such devices and methods would be particularly well-received if they offered the ability to lower a logging tool on a wireline while preventing the tool from becoming stuck in the wellbore.